As a device for reading images of a subject (document images), such as printing materials and photos, such image reading devices are in practical use as to read images with an image sensor while applying light from a light source to output image signals (for example, see PL1).
Image reading devices are widely used in the field of inspection devices for checking conditions of printed materials upon completion of printing, in addition to copiers and facsimiles (FAXs). In recent years, use of image reading devices is positively considered with regard to inspection on printed materials in which regular ink and special ink are used in combination. This case involves separate acquisition of document images corresponding to portions printed with regular ink and document images corresponding to portions printed with special ink.
As special ink, for example, such an ink is used in some cases as to be reactive only to non-visible light, e.g., infrared light and ultraviolet light, and incapable of being read by application of visible light. For this reason, an image reading device for obtaining document images with visible light and an image reading device for obtaining document images with non-visible light are installed independently of each other, and images needed are obtained accordingly by means of these image reading devices. However, cost is increased as a whole in case of installing discrete image reading devices, for the image reading devices are needed by the number corresponding to the kinds of inks.